Optimal Symmetric Ratcheting for Secure Communication

Abstract To mitigate state exposure threats to long-lived instant messaging sessions, ratcheting was introduced, which is used in practice protocols like Signal. However, existing generally come with a high cost. Recently, Caforio et al. proposed pragmatic constructions, compose weakly secure ‘light’ protocol and strongly ‘heavy’ protocol, order achieve so-called on-demand. The light they has still complexity. In this paper, we propose the lightest possible could imagine, essentially encrypts then hashes secret key. We prove it standard model by introducing new security notion, relates symmetric encryption key updates hashing. Our composes well generic transformation techniques offer performance at same time. second step, another based on newly defined integrated primitive, extending one-time authenticated an additional output block as for next message. instantiate primitive firstly from any associated data, efficient instantiation using advanced (AES) update AES-Galois/Counter mode of operation encrypt decrypt messages.